//全屏函数
function fullscreen(){
  if (document.fullscreenElement ||
          document.mozFullScreenElement ||
          document.webkitFullscreenElement ||
          document.msFullscreenElement) {
      if (document.exitFullscreen) {
          document.exitFullscreen();
      } else if (document.mozCancelFullScreen) {
          document.mozCancelFullScreen();
      } else if (document.webkitExitFullscreen) {
          document.webkitExitFullscreen();
      } else if (document.msExitFullscreen) {
          document.msExitFullscreen();
      }
  } else {
      if (document.documentElement.requestFullscreen) {
          document.documentElement.requestFullscreen();
      } else if (document.documentElement.mozRequestFullScreen) {
          document.documentElement.mozRequestFullScreen();
      } else if (document.documentElement.webkitRequestFullscreen) {
          document.documentElement.webkitRequestFullscreen();
      } else if (document.documentElement.body.msRequestFullscreen) {
          document.documentElement.body.msRequestFullscreen();
      }
  }
}
export {
  fullscreen
}